Re: [Qemu-trivial] [Qemu-devel] [PATCH v3 6/9] arm: clarify the use of muldiv64()

[Peter Crosthwaite]

On Thu, Aug 27, 2015 at 12:33 PM, Laurent Vivier <address@hidden> wrote:
> muldiv64() is used to convert microseconds into CPU ticks.
>
> But it is not clear and not commented. This patch uses macro
> to clearly identify what is used: time, CPU frequency and ticks.
> For an elapsed time and a given frequency, we compute how many ticks
>  we have.
>
> Signed-off-by: Laurent Vivier <address@hidden>

Reviewed-by: Peter Crosthwaite <address@hidden>

> ---
> v2: replace "arm: remove muldiv64()"
>  target-arm/helper.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 7df1f06..4455761 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -12,6 +12,8 @@
>  #include <zlib.h> /* For crc32 */
>  #include "exec/semihost.h"
>
> +#define ARM_CPU_FREQ 1000000000 /* FIXME: 1 GHz, should be configurable */
> +
>  #ifndef CONFIG_USER_ONLY
>  static inline bool get_phys_addr(CPUARMState *env, target_ulong address,
>                                   int access_type, ARMMMUIdx mmu_idx,
> @@ -678,8 +680,8 @@ void pmccntr_sync(CPUARMState *env)
>  {
>      uint64_t temp_ticks;
>
> -    temp_ticks = muldiv64(qemu_clock_get_us(QEMU_CLOCK_VIRTUAL),
> -                          get_ticks_per_sec(), 1000000);
> +    temp_ticks = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
> +                          ARM_CPU_FREQ, NANOSECONDS_PER_SECOND);
>
>      if (env->cp15.c9_pmcr & PMCRD) {
>          /* Increment once every 64 processor clock cycles */
> @@ -717,8 +719,8 @@ static uint64_t pmccntr_read(CPUARMState *env, const 
> ARMCPRegInfo *ri)
>          return env->cp15.c15_ccnt;
>      }
>
> -    total_ticks = muldiv64(qemu_clock_get_us(QEMU_CLOCK_VIRTUAL),
> -                           get_ticks_per_sec(), 1000000);
> +    total_ticks = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
> +                           ARM_CPU_FREQ, NANOSECONDS_PER_SECOND);
>
>      if (env->cp15.c9_pmcr & PMCRD) {
>          /* Increment once every 64 processor clock cycles */
> @@ -738,8 +740,8 @@ static void pmccntr_write(CPUARMState *env, const 
> ARMCPRegInfo *ri,
>          return;
>      }
>
> -    total_ticks = muldiv64(qemu_clock_get_us(QEMU_CLOCK_VIRTUAL),
> -                           get_ticks_per_sec(), 1000000);
> +    total_ticks = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
> +                           ARM_CPU_FREQ, NANOSECONDS_PER_SECOND);
>
>      if (env->cp15.c9_pmcr & PMCRD) {
>          /* Increment once every 64 processor clock cycles */
> --
> 2.1.0
>
>